Densitometers can measure the passage of light through a transparent or semitransparent material. The measured density of a measurable substance is typically determined by measuring attenuation in the intensity of light which reaches the optical detector of the densitometer after passing through the measurable substance, the measurement being related to the absorption of light of the measurable substance.
Most densitometers include a light source, often a laser, aimed at a photoelectric cell, arranged with a gap in between so as to allow placing the measurable substance in the gap. The electric current that is generated by the photovoltaic cell of the densitometer is typically directly proportional to the intensity of the incident light, and thus the optical density of the measurable substance is determined by comparing the generated current with a reference current value that corresponds to the passing of light from the light source to the photovoltaic cell when the gap is kept empty.
A multi-component device may be considered kinematically constrained when each of the degrees of freedom is fully constrained and typically, none are over-constrained.
Kinematic couplings or joints may typically refer to machined mechanical contacts. In some examples, the kinematic couplings may involve a kinematic tooth configured to be inserted into a kinematic slot.
Quasi-kinematic constraints typically allows for a small amount of over-constraint while providing high precision. Quasi-kinematic coupling typically includes contacts between corresponding machined mechanical contacts. In some examples, these contacts may be a cylinder on a flat surface or a ball in a cone. Typically, in contrast to kinematic coupling, by reducing the surface contact to a line, over-constraint may, in some examples, be reduced from three degrees of freedom to two degrees. Since line contacts typically only weakly over-constrain an interface between to mechanical contacts, more deterministic relationships may be able to be formed. These more deterministic relationships may provide improved repeatability in the construction of a mechanical unit or device.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.